FIGS. 6A to 6C illustrate a conventional gear wrench with an angle formed between its head and tail, such that its tail inclines upwards with respect to its head. The purpose for providing the inclination is to form a height difference between its tail and open wrenching end to allow easy gripping by an operator. However, such a design fails to meet ergonomics because the operator's hand would need to incline for a certain degree along with the inclined tail.
In addition, due to the inclination of the wrench, when the operator applies a force to cause its head to rotate a fastener (such as bolt), the operator's hand tends to turn the force of application in a horizontal direction so as to result in a vertical component of force Fh and a horizontal component of force Fv. The horizontal component of force Fh will generate a torque along with the wrench to be transmitted to the fastener for tightening or loosening purpose, and is an effective component of force.
However, the vertical component of force Fh is an ineffective component of force and is somewhat hazardous because it may cause the wrench to be lifted up (FIG. 6B) or pressed down (see FIG. 6C). At the same time, in application of the force by the operator, the inclination of the wrench may easily cause change in orientation of vertical component of force. In case the force is not applied to a central axis of the wrench, the vertical component may also cause flipping of the wrench (see FIGS. 6D and 6E). The above phenomena may all cause separation of the gear wrench from the bolt, thereby causing accidents and occupational hazards.